As the Minamata Convention, a legally binding treaty on controlling mercury (Hg) has entered into force on the 16th August of this year, there have also been paradigm-changing developments in our knowledge about mercury’s effects on the health of human and animal communities.
A recent study has overturned the viewpoint that the most affected species by mercury are large aquatic piscivorous species. It shows that small invertivorous passerine birds collect especially high levels of mercury, particularly if they are in contaminated areas, and if they eat spiders and are hence very high on the food chain.
This study is based on decades of work on mercury pollution by Prof. QIU Guangle at the Institute of Geochemistry, Chinese Academy of Sciences (IGCAS). His work focuses on the levels and sources of mercury contamination in China and specifically Guizhou, and the potential risks for human exposure to mercury especially through rice. He has continuing research projects looking at wildlife exposure to mercury at Wanshan Mercury Mining District. Even compared to other contaminated areas in Guizhou, Wanshan has extraordinary high levels of mercury in soil, water and air samples.
Prof. QIU Guangle teamed up with international researchers to explore the levels of mercury in animals in Wanshan area, and whether rice cultivation may serve as an important source of exposure for animals, as it does for humans. This team has the diverse experience to collect physical and biological samples. Both Prof. Goodale and Mr. Kasun Abeysinghe have widespread knowledge in ecology, animal behavior and conservation biology. This work represents an international team, with researchers from New Zealand, Sweden and Canada, with each member adding unique contributions and perspectives.
The team is excited to present data showing that animals near rice paddies can accumulate mercury at previously unheard of levels. The levels in passerine birds were particularly high to the knowledge the highest measurements ever in bird feathers in Asia – and at the levels of adverse effects even when those are estimated for larger, non-passerine species (~40 mg/kg).
In addition, rice pests and granivorous species had elevated total Hg (THg) readings, demonstrating the link to rice; spiders were also particularly high and appear to be the vector of mercury to the animals at the top of the food chain.
Particularly concerning is that invertivorous birds at control site, where deposition is likely to be the source of Hg, had lower, yet still substantial levels of mercury, that might reach levels of adverse effects for passerines (~10 mg/kg).
The source of Hg there is likely atmospheric deposition, and this result suggests there could be significant population level health effects and consequent biodiversity loss in sensitive ecosystems in Asia.
The researchers believe multinational biomonitoring with invertivorous songbirds is necessary for assessing this risk and is critical for successful implementation of the Minamata Convention on Mercury. Furthermore, the animal data collected in this study can be used to guide human health policy in the mining region.
Their research results titled "
Mercury flow through an Asian rice-based food web" was published in Environmental Pollution.
